More extensibile nuget based adapter settings

[AbhitejJohn]

Currently settings for nuget based data collectors are difficult to specify given that the code base entry cannot be a fixed path on disk.
Currently this is achieved by adding in a check in the vstest code to fix this up based on a build property that supplies test adapter paths through a VSTestTestAdapterPath build property.
We'd either want to have an inbuilt mechanism that falls back to adapter paths if a codebase entry is not a path or we'd want to have a better mechanism for adapters to specify a full file path.
Originated from a discussion at #2288

[MarcoRossignoli]

For the completeness at the moment there is a fallback inside inproc collector based on list of paths passed to host before testing

vstest/src/Microsoft.TestPlatform.CrossPlatEngine/DataCollection/InProcDataCollectionExtensionManager.cs

Line 244 in ca24ad0

private string GetCodebase(string codeBase)

PR #2288 remove custom code that pass coverlet.collector.dll base path.

[nohwnd]

This is a new feature and won't be implemented, we are focusing on adding new features to Testing.Platform instead. https://aka.ms/testingplatform